Ripple wavelength, amplitude, and configuration in lyotropic liquid crystals as a function of effective headgroup size

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Abstract
We present differential scanning calorimetry (DSC) and freeze-fracture electron micrographs of the P03B2' phase of dimyristoylphosphatidylcholine (DMPC) multilamellar liposomes in excess water with varying fractions of N-methyl substituted dimyristoylphosphatidylethanolamine (DMPE * ). DMPE * was chosen as a dopant to eliminate the mismatch between the areas of the polar headgroup and the hydrocarbon chains of DMPC. DSC results show that the P03B2' phase disappears at a DMPE * mole fraction of about 0.15. Two distinct ripple configurations are observed at all DMPE * fractions that exhibited a P03B2' phase ; an asymmetric ripple of wavelength 12.0 nm and amplitude less than 6 nm and a symmetric ripple of incommensurate wavelength 22.0 nm and an amplitude of at least 9 nm. Defects, such as disclinations and grain boundaries are stabilized by DMPE *, but the ripple shapes, wavelength and amplitudes are unaffected. DMPE* also seems to prevent the annihilation of the ripples below the pretransition. The results are discussed in relation to continuum